Gamasutra posted a great breakdown of one of my favorite series, Dragon Quest (née Dragon Warrior), all in a mere 10 pages — lengthy, but worth a read through if you're a fan of the games. After a flying introduction on why Dragon Quest has been very popular, the author takes a detailed look at each installment of the series.
Throughout its life, Final Fantasy constantly reinvented itself, keeping certain aspects but bucking trends with each iteration. On the other hand, Dragon Quest has been strongly about keeping with tradition. All of them take place in the same European-style medieval world. All of them feature the same key staff members -- Horii, Toriyama, and Sugiyama. As a result, the method of storytelling, the characters, the battle system and the style of music is pretty much the same throughout. It's a series that prides itself not only on familiarity and nostalgia, but also in its consistency.
I'm not sure Final Fantasy deserves credit for 'constantly reinvent[ing]itself,' since I do wonder how many mopey, bizarrely coiffed heroes of dubious renowned one company can churn out, but be that as it may — it's a fun and nostalgic look back at one prolific series.
The History of Dragon Quest [Gamasutra]